Various yardsticks suggest the U.S. military — or at least the officer corps, which accounts for 17% of the 1.4 million–strong active-duty force — leans Republican.

The nation’s 24 million troops and veterans account for about 10% of the nation’s potential voters, but they’re not the monolithic bloc many believe.

Outsiders tend to think the U.S. military is made up entirely of blood-and-gut conservatives, à la John Wayne, but there’s little real evidence to back that up. When the Iraq war was launched, the consensus among U.S. military officers interviewed at the time was that 1 in 3 officers opposed it, suggesting they all weren’t gun ho.

“The officers by and large are more conservative,” says an Army sergeant just back from Afghanistan. “But the enlisted tend to be more liberal.” Of course, with fewer than 1 in 5 of those in uniform an officer, there’s a lot more enlisted voters.

But the U.S. military plainly tilts toward the GOP. That’s largely because today’s military is an all-volunteer force increasingly drawn from the Sun Belt, where the Pentagon has focused its recruiting efforts since the draft ended 40 years ago. And traits the military prizes — like aggressiveness and respect for authority — tend to be more pronounced in conservatives.

While the U.S. military assesses its force every which way — here’s the most recent demographic report — it steers clear of asking about troops’ political views. Military leaders have insisted for years that politics has no role in the U.S. military and that the only way to remain trustworthy is to stay resolutely nonpartisan.

“Former and retired service members, especially generals and admirals, are connected to the military service for life,” Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, said in June. “When the title or uniform is used for partisan purposes, it can erode the trust relationship.”

Of course, not everyone — particularly those who have retired — agrees with Dempsey. More than 300 retired generals and admirals have endorsed Republican Mitt Romney’s bid for the presidency. They’re slated to take this advertisement in Monday’s Washington Times newspaper boasting of their support. President Obama hasn’t released such a list, although he pocketed the recent endorsement of Colin Powell, a retired Army general and former Secretary of State.

The independent Military Times newspaper conducted a voluntary survey among its members that shows them supporting Romney over Obama by a margin greater than 2-to-1. But the newspaper’s subscribers are older and more senior in rank than most of those in the military as a whole, and the fact that it’s a self-selected sample can further distort its findings.

Indeed, there has been a conservative drift among U.S. military officers since the draft ended. In a 2009 survey of 4,000 Army officers, Heidi Urben, an active-duty officer and doctoral candidate at Georgetown University, found that from 1976 to 1996, the share of senior military officers identifying itself as Republican jumped from one-third to two-thirds, while those claiming to be moderates fell from 46% to 22%.

Senior military officers who described themselves as liberal fell from 16% in 1976 to 3% in 1996. Urben found that younger officers leaving the Army were far more likely to identify themselves as Democrats than those opting to stay, which would tend to make the more senior ranks increasingly Republican.

“Past surveys have shown senior military officers to generally be conservative and identify with the Republican Party, a trend which has solidified with the advent and professionalism of the all-volunteer force,” Urben wrote in her 2010 dissertation. “Meanwhile, recent surveys suggest that the officer corps is more likely to be conservative and Republican than most enlisted soldiers, an important distinction to keep in mind, considering enlisted soldiers outnumber officers by 4 to 1 in the Army.”

Pew, 2011

A Pew survey released last year showed post-9/11 veterans’ political leanings are the reverse of the public they’re serving: 36% described themselves as Republicans, and 21% as Democrats; 34% of the public said they were Democrats, and 23% Republican. Six in 10 vets say they’re more patriotic than the average American.

But there is conflicting evidence. The Center for Responsive Politics reported last month that self-described military personnel had donated $678,611 to Obama, 85% more than the $398,450 the Romney campaign has collected.

Back to that sergeant who has just returned from Afghanistan. While the troops are split over whom they’re supporting for President, he says, they’re united on one thing: they’re upset that neither their current Commander in Chief, nor his prospective replacement, ever served a day in a U.S. military uniform. “That,” he says with a pained expression on his dogface, “is something they agree on.”